The present invention relates to electrical switch assemblies, and particularly to a switch assembly capable of being tested without disconnecting the switch from an electrical circuit or removing the switch assembly from its mounted position.
It is normally desired to mount switch assemblies more or less permanently as part of an electrical circuit, yet it occasionally becomes necessary to test the operation of the included switches individually. It is usually desired to mount switches in a manner which protects and conceals circuit connection terminals and protects electrical conductors from inadvertent short circuits, in the case of industrial position controlling applications, and which protects connections from tampering, in the case of security alarm circuits.
Previously known switch assemblies designed for mounting on a surface such as a wall often have covered circuit connection terminals, to protect against tampering or inadvertent short circuiting. Access to the connection terminals requires removal of at least a portion of such a housing from its mounting position. Other known switch housings are designed for mounting in a recessed position, sometimes having one surface of the switch housing substantially flush with the surrounding wall or other surface.
Once installed, when such switch assemblies comprise magnetically actuated reed switches, as in the case of proximity switch assemblies used for industrial position controlling applications and to monitor the status of doors and windows, etc., little maintenance is normally required. Testing is necessary, however, during initial installation, or in the case of malfunction, since electrical overloading may occasionally cause switch contacts to fuse together. More frequently, a magnetic reed switch may fail to actuate because the actuating magnet has been displaced from its proper location.
In applications such as physical security monitoring alarm systems, several magnetically actuated switches are frequently interconnected in one series circuit requiring each switch in the circuit to be closed in order for the system to indicate a normal condition. When one switch of the circuit fails to close, even though all doors, windows, and the like being monitored by the alarm system are in their proper locations, it has previously been very difficult to test the several switches of the system to determine which switch is malfunctioning.
Testing of switches in a series loop circuit has previously required disconnection of the individual switches from a circuit. Quite often removal of a switch from its mounted location, particularly if the switch is mounted in a flush or recessed location, results in damage to a switch which was previously undamaged. Additionally, removal and replacement of switches frequently results in damage to the appearance of the switch location. Testing of a circuit may also require establishing some form of electrical communication between a person operating a switch and another person monitoring operation of the switch at a remote junction box.
While it is possible to individually check each switch of a series circuit if conductors are provided from each individual switch to a central connection box, using a wiring scheme called "home running," this requires undesirably large and costly amounts of wire, as well as provision of an otherwise unnecessary junction box.
A somewhat less expensive wiring scheme is called "zoning." By providing several "zones," series connected loops containing only a few switches in each loop, a malfunction can be traced to a single loop. "Zoning," however, still requires disconnection for testing of each switch in the malfunctioning "zone," until the defective switch has been found.
Similar difficulties are presented when a group of several parallel connected switches are normally open, but one switch of the group remains closed as a result of a malfunction. This condition has also previously required disconnection of each switch to locate the malfunction.
What is needed, therefore, is a switch assembly capable of being mounted in a way to present a pleasant appearance, including a housing which protects the switch and prevents undesired access to the circuit of which the switch is a part, but which permits local electrical testing of the operation of each switch in its installed position without electrically disconnecting the switch from its circuit.